1. Field of the Invention
The present invention relates in general to elastic strips of a keyboard and a method for producing the same.
2. Description of the Related Art
Referring to FIG. 1, a conventional keyboard of a notebook includes a plurality of key caps 11 (only one key cap is shown in the figure), a plurality of cap supports 12 (only one cap support is shown in the figure), an elastic sheet 13, a circuit membrane assembly 14 and a foundation sheet 15.
The foundation sheet 15 is a metal sheet on which a plurality of seats 151 and hooks 152 are formed by punching and pressing.
The circuit membrane assembly 14 includes three membrane layers, wherein a middle layer is sandwiched by two outer layers. On the outer layers are provided circuits, while on the middle layer are provided holes. By this arrangement, an electric conduction between the two circuits on the outer layers is induced when the outer layers are compressed to contact each other through the holes of the middle layer. Furthermore, a plurality of through holes 141 are provided on the circuit membrane assembly 14. That is, the through holes 141 penetrate the outer layers and the middle layer of the circuit membrane assembly 14.
The elastic sheet 13 is made of rubber and is formed by using the Injection Molding Method. The elastic sheet 13 has a sheet-like body 130, a plurality of elastic domes 131, connecting portions 133 and through holes 132, wherein the connecting portions 133 connect the elastic domes 131 and the sheet-like body 130. Further referring to FIG. 2, the elastic dome 131 has a plunger 1311 inside.
The cap support 12 has a first linking bracket 121 and a second linking bracket 122. The shaft portions 1221 of the second linking bracket 122 are inserted into the holes 1211 of the first linking bracket 121 so that the first linking bracket 121 and the second linking bracket 122 are hinged together. Such a structure is so called xe2x80x9cscissors-type support structurexe2x80x9d. Furthermore, the first linking bracket 121 has shaft rods 1212, 1213 and the second linking bracket 122 has shaft rods 1222 on their corners.
Referring to FIG. 3, the key cap 11 has hook portions 111 and holding portions 112, 113 on its bottom surface.
Now, the way of assembling the conventional keyboard is described. The circuit membrane assembly 14 and the elastic sheet 13 are put on the foundation sheet 15, with the seats 151 and hooks 152 of the foundation sheet 15 sticking out through till the through holes 141 of the circuit membrane assembly 14 and the through holes 132 of the elastic sheet 13. The key cap 11 is mounted on the foundation sheet 15 via the cap support 12, wherein the shaft rods 1212 are inserted into the seats 151 so that the first linking bracket 121 is rotatable with respect to the foundation sheet 15, and the narrow portion 1223 of the second linking bracket 122 is hooked by the hook 152 of the foundation sheet 15 so that the second linking bracket 122 is also rotatable with respect to the foundation sheet 15. Furthermore, the shaft rods 1213 of the first linking bracket 121 are held by the hook portions 111, and the shaft rods 1222 of the second linking bracket 122 are held by the holding portions 112, 113.
In operation, the user pushes down the key cap 11 so as to compress the elastic dome 131. Then, the plunger 1311 of the elastic dome 131 pushes against the circuit membrane assembly 14 so that an electric conduction is induced to send out a corresponding signal.
In manufacture, however, the elastic sheet 13 of the conventional keyboard of a notebook has the following flaws: (1) The elastic sheet 13 is made of rubber and formed by the Injection Molding Method. Building the mold for the elastic sheet 13 is expensive. In addition, manufacturers need to build new molds for elastic sheets with new specifications because different kinds of keyboards are provided with different elastic sheets. Therefore, the cost for manufacturing keyboards is high. (2) A mold is built when a keyboard of a new specification is developed. However, if the elastic sheet 13 produced by using the mold has dimensions outside the tolerance, then the mold needs to be rebuilt. Then, the cost of developing the new keyboard is raised, the time for developing the new keyboard is elongated and the mass production of the new keyboards is delayed. It is disadvantageous for commercial competition. (3) The elastic sheet 13 has a plurality of rows of elastic domes 131 formed thereon. The distances between the rows of elastic domes 131 must comply with the distances between the key caps of the keyboard. Therefore, the materials connected between the rows of elastic domes 131 can not be eliminated. In other words, the weight of the elastic sheet 13 and the material cost cannot be reduced. (4) The user pushes down the key caps while typing. Referring to rig. 4, the stroke for the key cap 11 to contact the elastic sheet 13 is xe2x80x9cLxe2x80x9d. For a conventional keyboard, however, the stroke generally is not long enough for the user to feel comfortable in operation. Referring to FIGS. 5A and 5B, a possible way to increase the stroke is to provide rectangular grooves 134 around the plunger 131. However, this arrangement reduces the thickness of the elastic sheet under the grooves to xe2x80x9cHxe2x80x9d so that the resistance of the mold cavity to the flow of the molten material is increased. Then, filling the mold cavity at the positions corresponding to the elastic domes tends to be incomplete.
An object of the present invention is to provide a means that solves the above-mentioned problems.
In the present invention, an elastic sheet is produced by using a mold, wherein the elastic sheet has a plurality of rows of elastic domes formed thereon. Then, the elastic sheet is cut into a plurality of elastic strips, each of which has only one row of elastic domes. Then, the elastic strips are disposed on keyboards.
To develop keyboards with new specifications, common portions of the new keyboard can use molds with prevailing specifications. Thus, only the molds for the elastic strips of new specifications need to be developed, and the cost for developing a new keyboard is therefore greatly reduced.
It is understood that only the molds for the new specifications need to be developed. If the development fails, the influences are local rather than overall. The engineers can fix the mistakes very soon so as to mass-produce the new keyboards in time. The present invention is advantageous for commercial competition.
In the present invention, the elastic sheets are cut into a plurality of elastic strips. Thus, the distances between the rows of the elastic domes on the elastic sheets do not need to comply with the distances between the key caps of the keyboards. The materials connected between the rows of elastic domes are reduced. And the material cost and the weight of the keyboard are reduced.
In the present invention, recesses are provided on the elastic strips and between the elastic domes to increase the stroke for the key caps to contact the elastic strips. While filling the mold cavity, the arrangement of the recesses does increase the resistance to the flow of molten material. However, the molten material can bypass the arrangement of the recesses so that the whole mold cavity is filled with molten material.